Showing papers on "Femtosecond pulse shaping published in 1985"

Control and measurement of ultrashort pulse shapes (in amplitude and phase) with femtosecond accuracy

Abstract: The performances of a tunable femtosecond dye laser are analyzed using accurate correlation techniques. The source is a passively mode-locked dye laser, of which both the frequency and frequency modulation are controlled by one or two intracavity prisms. Interferometric second-order autocorrelations, with a peak-to-background ratio of 8 to 1, are used simultaneously with the conventional intensity autocorrelation and the pulse spectrum to determine the pulse shape. The main advantages of the interferometric autocorrelations are that they provide phase information otherwise not available, and they are more sensitive to the pulse shape than the intensity autocorrelation. The phase sensitivity is demonstrated in an analysis of the Gaussian pulses with a linear frequency modulation. Analytical expressions for the envelopes of the interferometric autocorrelations of typical pulse shapes are provided for quick pulse shape identification. A numerical method is used to analyze the more complex pulse shapes and chirps that can be produced by the laser. A series of examples demonstrates the control of this laser over various pulse shapes and frequency modulations. Pulse broadening or compression by propagation through glass is calculated for the pulse shapes determined from the fittings. Comparisons of autocorrelations and cross correlations calculated for the dispersed pulses, with the actual measurements, demonstrate the accuracy of the fitting procedure. The method of pulse shape determination demonstrated here requires a train of identical pulses. Indeed, it is shown that, for example, a train of unchirped pulses randomly distributed in frequency can have the same interferometric autocorrelation than a single chirped pulse. In the case of the present source, a comparison of the pulse spectrum, with that of the second harmonic, gives an additional proof that pulse-to-pulse fluctuations are negligible.

Optical wave breaking of pulses in nonlinear optical fibers

Abstract: A new effect appears in femtosecond optical pulse compression, using single-mode fibers, that we describe as optical wave breaking. In the fiber, frequency-shifted light in the leading and trailing edges of a pulse overtakes unshifted light in the pulse tails. Mixing of these overlapping frequency components generates sidelobes on the pulse spectrum. The effect often leads to computational instabilities, but careful numerical simulations, including fiber loss, give results in excellent agreement with experiment.

Picosecond pulse shaping by spectral phase and amplitude manipulation.

Abstract: The temporal profile of ultrashort optical pulses may be tailored by physically manipulating the phase and the amplitude of frequency components that are spatially dispersed within a grating pulse compressor. Arbitrary pulse shapes may be synthesized subject only to the usual restrictions imposed by finite bandwidth and spatial resolution. We demonstrate this technique by generating a burst of evenly spaced picosecond pulses, a pulse doublet with odd field symmetry, and a burst of evenly spaced pulse doublets with odd field symmetry.

Optical generator and detector of stress pulses

Abstract: An optical stress pulse generation and detection system for non-destructively measuring physical properties of a sample, which uses a pump beam having short duration radiation pulses having an intensity and at least one wavelength selected to non-destructively generate a stress pulse in a sample and directs the non-destructive pump beam to a surface of the sample to generate the stress pulse. The optical stress pulse generation and detection system also uses a probe radiation beam and guides the probe beam to a location at the sample to intercept the stress pulse. The change in optical constants induced by the stress pulse is detected by observing the probe beam after it intercepts the stress pulse.

Shaping optical pulses by amplitude and phase masking

Abstract: Embodiments of the present invention control, manipulate and tailor the shape of input optical pulses to produce substantially transform-limited output pulses which can be shorter than the input pulses. In embodiments of a first aspect of the present invention an input optical pulse is chirped, the chirped pulse is then passed through an optical component that spatially disperses the frequency components of the chirped pulse and partially compensates the chirp, the spatially dispersed frequency components are then passed through spatial amplitude and/or phase masks that control and/or adjust the amplitude and/or phase of the frequency components, and, finally, the masked components are passed through the first or a second optical component that returns the masked, spatially dispersed frequency components substantially to the spatial distribution of the input pulse while substantially completing the compensation of the chirp to form an output pulse.

Amplification of picosecond 10 µm pulses in multiatmosphere CO 2 lasers

Abstract: Picosecond pulses, generated by semiconductor switching (2-40 ps), have been regeneratively amplified to an energy density of ∼1.5 J/cm2in a multiatmosphere CO 2 laser. The characteristics of the amplified pulses have been investigated as a function of wavelength, pulse duration, and the pressure in the gain medium. Using a high-power pulse compression technique, 10 μm pulses as short as 600 fs have been obtained.

Intracavity chirp compensation in a colliding pulse mode‐locked laser using thin‐film interferometers

Abstract: Dielectric multilayer mirrors designed as Gires–Tournois interferometers have been used in a colliding pulse mode‐locked dye laser to study the influence of intracavity group velocity dispersion on the pulse formation. Simple angle tuning of the interferometric mirrors which is equivalent to a change of the net cavity dispersion resulted in a shift of the laser wavelength between 627 and 614 nm. Within this range stable operation with pulse durations of 130 fs or less and average output powers between 30 and 80 mW was obtained. The shortest pulse of 80 fs duration was found at 626 nm.

Dispersive effects in the reflection of femtosecond optical pulses from broadband dielectric mirrors

Abstract: The dispersive effects of high-reflectivity broadband mirrors on femtosecond optical pulses have been analyzed for three different multilayer structures. In each case the high-reflectivity zone can be divided into two different regions symmetrically located around the mirror central frequency: high-dispersion and low-dispersion regions. The calculated temporal behavior of the reflected pulse shows high distortion of the pulse profile, a frequency chirp, and a broadening as high as a factor of 5.6, due to a single reflection, within the high-dispersion region. The use of these types of mirror should therefore be strictly limited to their low-dispersion side.

All-fiber pulse compression at 1.32 μm

Abstract: We have constructed a pulse compressor using two different optical fibers. By adjusting the waveguide dispersion it has been possible to produce fibers with positive and negative dispersion at 1.32 μm. We have demonstrated the compression of 130-psec pulses down to our photodiode limit of 70 psec. This is supported by our calculations, which give a theoretical pulse width of 50 psec. This is the first reported demonstration of both an all-fiber pulse compressor and optical pulse compression at 1.32 μm.

Measurement of the phase of a frequency-swept ultrashort optical pulse

Abstract: We show theoretically and confirm experimentally that, by propagating a frequency-swept ultrashort pulse through an ensemble of two-level systems, it is possible to measure the time-dependent relative phase of the pulse with respect to that of the impact-excited oscillating resonant polarization. The phase is obtained from the intensity modulation of the pulse as measured by a cross-correlation technique.

Reduction of laser chirp in 1.5 μm DFB lasers by modulation pulse shaping

Abstract: The dynamic linewidth of 1.5 μm ridge waveguide DFB lasers is shown to be reduced by shaping the pulse of the laser modulating waveform. Pulse shaping is performed by a second-order network designed to cancel the small-signal laser resonance. Results demonstrate a dynamic linewidth reduction from 1.4 A to 0.55 A FWHM for a 500 ps pulse.

Femtosecond laser pulse compression using volume phase transmission holograms

Abstract: Combining holographic and femtosecond laser pulse compression technology, gigawatt peak power and 85-fsec bandwidth-limited laser pulses were obtained. Pulse compression was achieved using a pair of high diffraction efficiency volume phase transmission holographic gratings.

A pulsed laser system and method of operation

Abstract: A pulsed laser system (500) capable of operating in a plurality of modes for delivering a burst of laser pulses to a target (506) wherein the pulse width of the laser pulses are automatically controlled in response to the mode selected. A special calibration procedure allows the system to deter­ mine the pulse width and pulse repetition rate when the laser (200) is producing a predetermined power output level as measured by a power meter at the target site. Using cali­ brated pulse width and pulse repetition rate, the pulse width and pulse repetition rate of the laser pulses to be delivered to the target (506) for any particular treatment burst can be determined.

Advantages and Limits of Light Pulse Compression inside and outside the Laser Cavity

Abstract: Limits for the compression of frequency-modulated light pulses, the chirp of which is a result of non-linear optical interactions in non-resonant and resonant media, are dealt with. In extracavity pulse compressors with non-resonant, non-linear samples the minimum pulse duration decreases with increasing field strength of the input pulse, the maximum of which must be restricted to avoid high-order non-linear effects and optical damage. Compression down to about 5 fs seems to be possible. In intracavity pulse compression, successfully used for example in passively mode-locked lasers, the chirp is generated by quasi-resonant interaction between light pulses and saturable absorbers or depletable amplifiers. Here the minimum achievable pulse duration is limited mainly by the frequency-selective action of the quasi-resonant samples.

Femtosecond laser pulse measuring system

Abstract: A system for measuring laser pulse durations in the range of ten nanoseconds to one femtosecond to an accuracy of one femtosecond, includes a primary pulse sampler, a ten component beam splitter array, optical delay lines whose settings are microprocessor controlled, a ten section interaction chamber with ten sets of ion detectors and a pulse envelope and pulse energy display monitors. The system has applications in chemistry, calibration of fast timing circuits and in the development of short pulse lasers.

Intracavity self-phase modulation and pulse compression in mode-locked lasers

Abstract: We show that in the presence of a bandwidth-limiting component intracavity selfphase modulation in high power mode-locked and Q-switched lasers is accompanied by interesting pulse-shaping phenomena. If the phase modulation is properly controlled the pulse duration can approach the limit given by the frequency bandwidth of the laser. For example, for a Nd: YAG laser our calculations predict an intracavity pulse compression by approximately a factor of ten over the typical pulse duration of conventional mode-locking.

Picosecond Pulse Generation by Self-Phase Modulation in an Actively Mode-Locked and Q-Switched Phosphate Glass Laser

Abstract: The generation of 4 ps pulses by an actively mode-locked and Q-switched phosphate glass laser is reported. The pulse width is found to decrease rapidly after the peak of the Q-switched pulse train, accompanied by distortion of the pulse temporal profile from the initial Gaussian shape. Theoretical analysis demonstrates that pulse shortening takes place when the phase-modulated pulse passes through the etalon in the laser cavity. Modulation in the phase of the pulse is caused by the nonlinear refractive indices of the laser rod and the two acousto-optic elements used for mode-locking and Q-switching.

Large Signal Behaviour of Optical Pulse Generation in Q-switched GaAlAs/GaAs Injection Lasers

Abstract: A large-signal model for passively Q-switched laser structures, consisting of an amplifying and a saturable absorber region, is presented. The amplitude, pulse rate and pulse width of self-sustained pulsations are derived. A comparison with experimental results, obtained from double-contacted metal clad ridge waveguide lasers, is performed.

Pulse shaping with transmission lines

Abstract: A method and apparatus for forming shaped voltage pulses uses passive reflection from a transmission line with nonuniform impedance. The impedance of the reflecting line varies with length in accordance with the desired pulse shape. A high voltage input pulse is transmitted to the reflecting line. A reflected pulse is produced having the desired shape and is transmitted by pulse removal means to a load. Light activated photoconductive switches made of silicon can be utilized. The pulse shaper can be used to drive a Pockels cell to produce shaped optical pulses.

Measurement of the duration of high-power ultrashort optical pulses

Abstract: An analysis is made of sound generation in the interaction between two orthogonally polarized components of a high-power ultrashort light pulse in an anisotropic crystal exhibiting electrostriction. It is shown that the envelope of an acoustic pulse takes the form of the autocorrelation function of the complex amplitude of the ultrashort pulse and its duration is between 6 and 7 orders of magnitude greater than that of the ultrashort pulse.

Detection and reconstruction of ultrashort pulses by interference of spectrally dispersed light

Abstract: A detailed analysis is made of the recording and reconstruction of ultrashort light pulses by a spectroscopic method. The time profile of an ultrashort pulse is recorded as a spectrogram of the sum of reference and signal pulses. The recorded signal pulse can be reconstructed by illuminating a spectrogram with spectrally resolved radiation of the reference pulse.

On Noise and Fluctuations in a Synchronously Mode-Locked cw Laser System

Abstract: A single-shot and synchronously-scanned streak camera, autocorrelation and noise spectrum analysing techniques are utilized to study the output characteristics of synchronously mode-locked cw lasers. Four main conclusions are drawn: (i) the pulse train from a synchronously-pumped dye laser reveals, besides phase jitter, considerable pulse shape fluctuations; (ii) autocorrelation measurements may be highly misleading when actual pulse shapes are considered; (iii) both the phase jitter and pulse shape fluctuations of the dye laser output are caused by the phase fluctuations of the pumping ion laser pulse train; (iv) the phase jitter of the ion laser proceeds from the fluctuations in the cavity roundtrip time with a characteristic time of about 5 μs. Under optimum conditions the rms noise of the dye laser output was 2% and the phase jitter with respect to the rf sine drive of the acousto-optical mode-locker, ∼30 ps. A qualitative explanation fo the noise properties is given.